A dock leveler typically includes a frame or supporting structure mounted in a pit or depression in the loading dock. The rear end of a ramp or deck plate is pivotally mounted to the supporting structure so that the ramp is movable between an inclined position and a declined position relative to the horizontal loading dock.
An extension lip is commonly pivotally mounted to the forward end of the ramp, and is movable between a downwardly hanging pendant position and an extended position in which the lip forms an extension to the ramp.
After a vehicle (e.g., a truck or trailer) has parked in front of the loading dock in preparation for a loading or unloading operation, the ramp of the dock leveler is raised to its inclined position. As the ramp is moved, the lip is pivoted outwardly to its extended position. When the ramp is lowered, the extended lip engages the bed of the truck to support the ramp such that the ramp and the lip in combination bridge the gap between the loading dock and the truck bed. After the loading or unloading operation is completed, the ramp can be raised and the lip falls by gravity to its pendant position. The ramp is then lowered to a stored, horizontal position and the truck can then pull away from the loading dock.
Some dock levelers also include run-off guards that provide a barrier at the outer end of the dock levelers to prevent loading equipment such as a forklift from rolling off of the dock. Run-off guards used on conventional dock levelers are movable between a raised position that forms a barrier and a lowered position that allows loading equipment to freely pass over the run-off guard. The simplest method for raising the run-off guard utilizes a run-off guard that is integral with the lip, as disclosed in German Patent No. 2634652. In this design, the run-off guard is raised when the lip is folded into the stored or pendant position, and the run-off guard is lowered when the lip is raised to the extended position. Another common method includes a run-off guard that is a separate component from the lip, but that is mechanically coupled to the lip such that the movement of the lip actuates the movement of the run-off guard. Such a design is disclosed in U.S. Pat. No. 5,333,339. These methods, however, do not facilitate end loading, which is necessary when cargo placed at the rear of the trailer prevents the lip from being extended on the bed of the trailer. Since the lip must remain lowered during end loading, the raised run-off guard usually prevents access to the cargo within the trailer.
Other devices lower the barrier independently of the lip to allow for end loading. Some devices require an actuator such as a hydraulic cylinder, while other passive devices are moved by springs and the like. One example of a passive device is shown in U.S. Pat. No. 3,486,181 that discloses a upwardly-biased barrier that is raised by releasing a latch mechanism used to hold the barrier in the lowered position. Another example is U.S. Pat. No. 5,553,343 that discloses a run-off guard that is actuated by a cam that is rotated in response to the raising and lowering of the ramp.